I am new to HT and am looking at two Yamaha receivers, the RXV-520 and the RXV-620. The 620 is listed with 20 more watts per channel (100 vs. 80). Besides that, the only other differences that I can see are that the 620 has on screen display, component video switching, and 5 channel stereo. I'm not sure what component video switching or 5 channel stereo are. Do I need them? Is the 620 worth the extra 100 bucks? Any insight would help.